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<div class="section">
<div class="titlepage"><div><div><h2 class="title" style="clear: both">
<a name="spirit.preface"></a><a class="link" href="preface.html" title="Preface">Preface</a>
</h2></div></div></div>
<div class="blockquote"><blockquote class="blockquote"><p>
        <span class="emphasis"><em><span class="quote">“<span class="quote">Examples of designs that meet most of the criteria for "goodness"
        (easy to understand, flexible, efficient) are a recursive-descent parser,
        which is traditional procedural code. Another example is the STL, which is
        a generic library of containers and algorithms depending crucially on both
        traditional procedural code and on parametric polymorphism.</span>”</span></em></span>
        <span class="bold"><strong>--Bjarne Stroustrup</strong></span>
      </p></blockquote></div>
<h4>
<a name="spirit.preface.h0"></a>
      <span class="phrase"><a name="spirit.preface.history"></a></span><a class="link" href="preface.html#spirit.preface.history">History</a>
    </h4>
<h4>
<a name="spirit.preface.h1"></a>
      <span class="phrase"><a name="spirit.preface._emphasis_80s__emphasis_"></a></span><a class="link" href="preface.html#spirit.preface._emphasis_80s__emphasis_"><span class="emphasis"><em>80s</em></span></a>
    </h4>
<p>
      In the mid-80s, Joel wrote his first calculator in Pascal. Such an unforgettable
      coding experience, he was amazed at how a mutually recursive set of functions
      can model a grammar specification. In time, the skills he acquired from that
      academic experience became very practical as he was tasked to do some parsing.
      For instance, whenever he needed to perform any form of binary or text I/O,
      he tried to approach each task somewhat formally by writing a grammar using
      Pascal-like syntax diagrams and then a corresponding recursive-descent parser.
      This process worked very well.
    </p>
<h4>
<a name="spirit.preface.h2"></a>
      <span class="phrase"><a name="spirit.preface._emphasis_90s__emphasis_"></a></span><a class="link" href="preface.html#spirit.preface._emphasis_90s__emphasis_"><span class="emphasis"><em>90s</em></span></a>
    </h4>
<p>
      The arrival of the Internet and the World Wide Web magnified the need for parsing
      a thousand-fold. At one point Joel had to write an HTML parser for a Web browser
      project. Using the W3C formal specifications, he easily wrote a recursive-descent
      HTML parser. With the influence of the Internet, RFC specifications were abundent.
      SGML, HTML, XML, email addresses and even those seemingly trivial URLs were
      all formally specified using small EBNF-style grammar specifications. Joel
      had more parsing to do, and he wished for a tool similar to larger parser generators
      such as YACC and ANTLR, where a parser is built automatically from a grammar
      specification.
    </p>
<p>
      This ideal tool would be able to parse anything from email addresses and command
      lines, to XML and scripting languages. Scalability was a primary goal. The
      tool would be able to do this without incurring a heavy development load, which
      was not possible with the above mentioned parser generators. The result was
      Spirit.
    </p>
<p>
      Spirit was a personal project that was conceived when Joel was involved in
      R&amp;D in Japan. Inspired by the GoF's composite and interpreter patterns,
      he realized that he can model a recursive-descent parser with hierarchical-object
      composition of primitives (terminals) and composites (productions). The original
      version was implemented with run-time polymorphic classes. A parser was generated
      at run time by feeding in production rule strings such as:
    </p>
<pre class="programlisting"><span class="string">"prod ::= {'A' | 'B'} 'C';"</span>
</pre>
<p>
      A compile function compiled the parser, dynamically creating a hierarchy of
      objects and linking semantic actions on the fly. A very early text can be found
      here: <a href="http://spirit.sourceforge.net/dl_docs/pre-spirit.htm" target="_top">pre-Spirit</a>.
    </p>
<h4>
<a name="spirit.preface.h3"></a>
      <span class="phrase"><a name="spirit.preface._emphasis_2001_to_2006__emphasis_"></a></span><a class="link" href="preface.html#spirit.preface._emphasis_2001_to_2006__emphasis_"><span class="emphasis"><em>2001
      to 2006</em></span></a>
    </h4>
<p>
      Version 1.0 to 1.8 was a complete rewrite of the original Spirit parser using
      expression templates and static polymorphism, inspired by the works of Todd
      Veldhuizen (<a href="http://en.wikipedia.org/wiki/Expression_templates" target="_top">Expression
      Templates</a>, C++ Report, June 1995). Initially, the static-Spirit version
      was meant only to replace the core of the original dynamic-Spirit. Dynamic-Spirit
      needed a parser to implement itself anyway. The original employed a hand-coded
      recursive-descent parser to parse the input grammar specification strings.
      It was at this time when Hartmut Kaiser joined the Spirit development.
    </p>
<p>
      After its initial "open-source" debut in May 2001, static-Spirit
      became a success. At around November 2001, the Spirit website had an activity
      percentile of 98%, making it the number one parser tool at Source Forge at
      the time. Not bad for a niche project like a parser library. The "static"
      portion of Spirit was forgotten and static-Spirit simply became Spirit. The
      library soon evolved to acquire more dynamic features.
    </p>
<p>
      Spirit was formally accepted into <a href="http://www.boost.org/" target="_top">Boost</a>
      in October 2002. Boost is a peer-reviewed, open collaborative development effort
      around a collection of free Open Source C++ libraries covering a wide range
      of domains. The Boost Libraries have become widely known as an industry standard
      for design and implementation quality, robustness, and reusability.
    </p>
<h4>
<a name="spirit.preface.h4"></a>
      <span class="phrase"><a name="spirit.preface._emphasis_2007__emphasis_"></a></span><a class="link" href="preface.html#spirit.preface._emphasis_2007__emphasis_"><span class="emphasis"><em>2007</em></span></a>
    </h4>
<p>
      Over the years, especially after Spirit was accepted into Boost, Spirit has
      served its purpose quite admirably. <span class="bold"><strong><span class="emphasis"><em>Classic-Spirit</em></span></strong></span>
      (versions prior to 2.0) focused on transduction parsing, where the input string
      is merely translated to an output string. Many parsers fall into the transduction
      type. When the time came to add attributes to the parser library, it was done
      in a rather ad-hoc manner, with the goal being 100% backward compatible with
      Classic Spirit. As a result, some parsers have attributes, some don't.
    </p>
<p>
      Spirit V2 is another major rewrite. Spirit V2 grammars are fully attributed
      (see <a href="http://en.wikipedia.org/wiki/Attribute_grammar" target="_top">Attribute
      Grammar</a>) which means that all parser components have attributes. To
      do this efficiently and elegantly, we had to use a couple of infrastructure
      libraries. Some did not exist, some were quite new when Spirit debuted, and
      some needed work. <a href="http://www.boost.org/libs/mpl/index.html" target="_top">Boost.Mpl</a>
      is an important infrastructure library, yet is not sufficient to implement
      Spirit V2. Another library had to be written: <a href="../../../../../libs/fusion/doc/html/index.html" target="_top">Boost.Fusion</a>.
      Fusion sits between MPL and STL --between compile time and runtime -- mapping
      types to values. Fusion is a direct descendant of both MPL and <a href="../../../../../libs/tuple/index.html" target="_top">Boost.Tuples</a>.
      Fusion is now a full-fledged <a href="http://www.boost.org/" target="_top">Boost</a>
      library. <a href="../../../../../libs/phoenix/doc/html/index.html" target="_top">Boost.Phoenix</a>
      also had to be beefed up to support Spirit V2. The result is <a href="../../../../../libs/phoenix/doc/html/index.html" target="_top">Boost.Phoenix</a>.
      Last but not least, Spirit V2 uses an <a href="http://en.wikipedia.org/wiki/Expression_templates" target="_top">Expression
      Templates</a> library called <a href="../../../../../doc/html/proto.html" target="_top">Boost.Proto</a>.
    </p>
<p>
      Even though it has evolved and matured to become a multi-module library, Spirit
      is still used for micro-parsing tasks as well as scripting languages. Like
      C++, you only pay for features that you need. The power of Spirit comes from
      its modularity and extensibility. Instead of giving you a sledgehammer, it
      gives you the right ingredients to easily create a sledgehammer.
    </p>
<h4>
<a name="spirit.preface.h5"></a>
      <span class="phrase"><a name="spirit.preface.new_ideas__spirit_v2"></a></span><a class="link" href="preface.html#spirit.preface.new_ideas__spirit_v2">New
      Ideas: Spirit V2</a>
    </h4>
<p>
      Just before the development of Spirit V2 began, Hartmut came across the <a href="http://www.stringtemplate.org/" target="_top">StringTemplate</a> library that is
      a part of the ANTLR parser framework. <a href="#ftn.spirit.preface.f0" class="footnote" name="spirit.preface.f0"><sup class="footnote">[1]</sup></a> The concepts presented in that library lead Hartmut to the next
      step in the evolution of Spirit. Parsing and generation are tightly connected
      to a formal notation, or a grammar. The grammar describes both input and output,
      and therefore, a parser library should have a grammar driven output. This duality
      is expressed in Spirit by the parser library <span class="emphasis"><em>Spirit.Qi</em></span>
      and the generator library <span class="emphasis"><em>Spirit.Karma</em></span> using the same
      component infrastructure.
    </p>
<p>
      The idea of creating a lexer library well integrated with the Spirit parsers
      is not new. This has been discussed almost since Classic-Spirit (pre V2) initially
      debuted. Several attempts to integrate existing lexer libraries and frameworks
      with Spirit have been made and served as a proof of concept and usability (for
      example see <a href="http://www.boost.org/libs/wave/index.html" target="_top">Wave</a>:
      The Boost C/C++ Preprocessor Library, and <a href="http://spirit.sourceforge.net/repository/applications/slex.zip" target="_top">SLex</a>:
      a fully dynamic C++ lexer implemented with Spirit). Based on these experiences
      we added <span class="emphasis"><em>Spirit.Lex</em></span>: a fully integrated lexer library
      to the mix, allowing the user to take advantage of the power of regular expressions
      for token matching, removing pressure from the parser components, simplifying
      parser grammars. Again, Spirit's modular structure allowed us to reuse the
      same underlying component library as for the parser and generator libraries.
    </p>
<h4>
<a name="spirit.preface.h6"></a>
      <span class="phrase"><a name="spirit.preface.how_to_use_this_manual"></a></span><a class="link" href="preface.html#spirit.preface.how_to_use_this_manual">How
      to use this manual</a>
    </h4>
<p>
      Each major section (there are 3: <a class="link" href="qi.html" title="Qi - Writing Parsers">Qi</a>, <a class="link" href="karma.html" title="Karma - Writing Generators">Karma</a>, and <a class="link" href="lex.html" title="Lex - Writing Lexical Analyzers">Lex</a>)
      is roughly divided into 3 parts:
    </p>
<div class="orderedlist"><ol class="orderedlist" type="1">
<li class="listitem">
          Tutorials: A step by step guide with heavily annotated code. These are
          meant to get the user acquainted with the library as quickly as possible.
          The objective is to build the confidence of the user in using the library
          through abundant examples and detailed instructions. Examples speak volumes
          and we have volumes of examples!
        </li>
<li class="listitem">
          Abstracts: A high level summary of key topics. The objective is to give
          the user a high level view of the library, the key concepts, background
          and theories.
        </li>
<li class="listitem">
          Reference: Detailed formal technical reference. We start with a quick reference
          -- an easy to use table that maps into the reference proper. The reference
          proper starts with C++ concepts followed by models of the concepts.
        </li>
</ol></div>
<p>
      Some icons are used to mark certain topics indicative of their relevance. These
      icons precede some text to indicate:
    </p>
<div class="table">
<a name="spirit.preface.icons"></a><p class="title"><b>Table 1. Icons</b></p>
<div class="table-contents"><table class="table" summary="Icons">
<colgroup>
<col>
<col>
<col>
</colgroup>
<thead><tr>
<th>
              <p>
                Icon
              </p>
            </th>
<th>
              <p>
                Name
              </p>
            </th>
<th>
              <p>
                Meaning
              </p>
            </th>
</tr></thead>
<tbody>
<tr>
<td>
              <p>
                <span class="inlinemediaobject"><img src=".././images/note.png" alt="note"></span>
              </p>
            </td>
<td>
              <p>
                Note
              </p>
            </td>
<td>
              <p>
                Generally useful information (an aside that doesn't fit in the flow
                of the text)
              </p>
            </td>
</tr>
<tr>
<td>
              <p>
                <span class="inlinemediaobject"><img src=".././images/tip.png" alt="tip"></span>
              </p>
            </td>
<td>
              <p>
                Tip
              </p>
            </td>
<td>
              <p>
                Suggestion on how to do something (especially something that is not
                obvious)
              </p>
            </td>
</tr>
<tr>
<td>
              <p>
                <span class="inlinemediaobject"><img src=".././images/important.png" alt="important"></span>
              </p>
            </td>
<td>
              <p>
                Important
              </p>
            </td>
<td>
              <p>
                Important note on something to take particular notice of
              </p>
            </td>
</tr>
<tr>
<td>
              <p>
                <span class="inlinemediaobject"><img src=".././images/caution.png" alt="caution"></span>
              </p>
            </td>
<td>
              <p>
                Caution
              </p>
            </td>
<td>
              <p>
                Take special care with this - it may not be what you expect and may
                cause bad results
              </p>
            </td>
</tr>
<tr>
<td>
              <p>
                <span class="inlinemediaobject"><img src=".././images/alert.png" alt="alert"></span>
              </p>
            </td>
<td>
              <p>
                Danger
              </p>
            </td>
<td>
              <p>
                This is likely to cause serious trouble if ignored
              </p>
            </td>
</tr>
</tbody>
</table></div>
</div>
<br class="table-break"><p>
      This documentation is automatically generated by Boost QuickBook documentation
      tool. QuickBook can be found in the <a href="http://www.boost.org/tools/index.html" target="_top">Boost
      Tools</a>.
    </p>
<h4>
<a name="spirit.preface.h7"></a>
      <span class="phrase"><a name="spirit.preface.support"></a></span><a class="link" href="preface.html#spirit.preface.support">Support</a>
    </h4>
<p>
      Please direct all questions to Spirit's mailing list. You can subscribe to
      the <a href="http://boost.2283326.n4.nabble.com/spirit-general-f2672582.html" target="_top">Spirit
      General List</a>. The mailing list has a searchable archive. A search link
      to this archive is provided in <a href="http://boost-spirit.com" target="_top">Spirit</a>'s
      home page. You may also read and post messages to the mailing list through
      <a href="news://news.gmane.org/gmane.comp.spirit.general" target="_top">Spirit General
      NNTP news portal</a> (thanks to <a href="http://www.gmane.org" target="_top">Gmane</a>).
      The news group mirrors the mailing list. Here is a link to the archives: <a href="http://news.gmane.org/gmane.comp.parsers.spirit.general" target="_top">http://news.gmane.org/gmane.comp.parsers.spirit.general</a>.
    </p>
<div class="footnotes">
<br><hr style="width:100; text-align:left;margin-left: 0">
<div id="ftn.spirit.preface.f0" class="footnote"><p><a href="#spirit.preface.f0" class="para"><sup class="para">[1] </sup></a>
        Quote from http://www.stringtemplate.org/: It is a Java template engine (with
        ports for C# and Python) for generating source code, web pages, emails, or
        any other formatted text output.
      </p></div>
</div>
</div>
<table xmlns:rev="http://www.cs.rpi.edu/~gregod/boost/tools/doc/revision" width="100%"><tr>
<td align="left"></td>
<td align="right"><div class="copyright-footer">Copyright © 2001-2011 Joel de Guzman, Hartmut Kaiser<p>
        Distributed under the Boost Software License, Version 1.0. (See accompanying
        file LICENSE_1_0.txt or copy at <a href="http://www.boost.org/LICENSE_1_0.txt" target="_top">http://www.boost.org/LICENSE_1_0.txt</a>)
      </p>
</div></td>
</tr></table>
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